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The genomic signature of splicing-coupled selection differs between long and short introns.

ABSTRACT: Understanding the function of noncoding regions in the genome, such as introns, is of central importance to evolutionary biology. One approach is to assay for the targets of natural selection. On one hand, the sequence of introns, especially short introns, appears to evolve in an almost neutral manner. Whereas on the other hand, a large proportion of intronic sequence is under selective constraint. This discrepancy is largely dependent on intron length and differences in the methods used to infer selection. We have used a method based on DNA strand asymmetery that does not require comparison with any putatively neutrally evolving sequence, nor sequence conservation between species, to detect selection within introns. The strongest signal we identify is associated with short introns. This signal comes from a family of motifs that could act as cryptic 5' splice sites during mRNA processing, suggesting a mechanistic justification underlying this signal of selection. Together with an analysis of intron length and splice site strength, we observe that the genomic signature of splicing-coupled selection differs between long and short introns.

SUBMITTER: Farlow A

PROVIDER: S-EPMC3245539 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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The genomic signature of splicing-coupled selection differs between long and short introns.

Farlow Ashley A Dolezal Marlies M Hua Liushuai L Schlötterer Christian C

Molecular biology and evolution 20110830 1

Understanding the function of noncoding regions in the genome, such as introns, is of central importance to evolutionary biology. One approach is to assay for the targets of natural selection. On one hand, the sequence of introns, especially short introns, appears to evolve in an almost neutral manner. Whereas on the other hand, a large proportion of intronic sequence is under selective constraint. This discrepancy is largely dependent on intron length and differences in the methods used to infe ...[more]

PMID: 21878685

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Project description:Despite evolutionary biology's obsession with natural selection, few studies have evaluated multi-generational series of patterns of selection on a genome-wide scale in natural populations. Here, we report on a nine-year population-genomic survey of the microcrustacean Daphnia pulex. The genome-sequences of > 800 isolates provide insights into patterns of selection that cannot be obtained from long-term molecular-evolution studies, including the pervasiveness of near quasi-neutrality across the genome (mean net selection coefficients near zero, but with significant temporal variance about the mean, and little evidence of positive covariance of selection across time intervals), the preponderance of weak negative selection operating on minor alleles, and a genome-wide distribution of numerous small linkage islands of observable selection influencing levels of nucleotide diversity. These results suggest that fluctuating selection is a major determinant of standing levels of variation in natural populations, challenge the conventional paradigm for interpreting patterns of nucleotide diversity and divergence, and motivate the need for the development of new theoretical expressions for the interpretation of population-genomic data.SignificanceExcept for mono/oligogenic traits known in advance to be under strong selection, there is little information on genome-wide patterns of temporal dynamics of allele-frequency changes in well-defined and unmanipulated natural populations. A multi-year survey of a population of the microcrustacean Daphnia pulex provides insight into these matters. Genome-wide analysis of > 800 genetic isolates demonstrates that temporal variation in selection intensity is a major determinant of levels of nucleotide polymorphism and divergence. Most nucleotide sites experience fluctuating selection with mean selection coefficients near zero, with little covariance in the strength of selection across time intervals, and with selection distributed across large numbers of genomic islands of linked sites. These results raise challenges for the conventional interpretation of measures of nucleotide diversity and divergence as indicators of effective population sizes and intensities of positive/negative selection.

Dataset Information

The genomic signature of splicing-coupled selection differs between long and short introns.

Publications

The genomic signature of splicing-coupled selection differs between long and short introns.

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